Physicians and other medical practitioners are keenly interested in methods and apparatus for treating pathogenic microorganisms and viruses contained in a living human body. In addition, they are interested in treating host cells that undergo transformation into cancer cells.
A wide variety of treatments for tumors, including chemotherapy and photodynamic therapy (PDT), have been developed for this purpose. Chemotherapy treats tumors through chemicals which have been injected into the body to attack a particular type of cell. PDT treats a tumor by coating its surface with a dye, such as hemato porphyrine derivative (HPD), which responds to light by creating singlet oxygen species. These species destroy the tumor membrane structures.
Such chemically based treatments are necessarily limited to the use of chemicals which are generally toxic to only one type of cell. These techniques rely on the chemical being more toxic to the unwanted cell than to the body. This imposes severe restrictions on the chemicals which can be used.
Treatments for less massive undesirable cellular materials, such as viruses contained in bodily fluids, are also generally chemically based, since this is a very effective way to get the treatment to each of the targeted cells. For example, PDT can also be used to treat undesirable cellular material in blood.
Unfortunately, PDT has serious disadvantages. For example, those who are undergoing PDT must avoid exposure to sunlight for approximately two days after undergoing the treatment. In addition, chemotherapy and PDT also affect nontargeted cells.
As disclosed in U.S. Pat. No. 4,395,397, Shapiro has investigated using fluorescence from tagged cells to trigger a pulsed laser which killed the fluorescing cells. However, to the applicant's knowledge, no one has investigated using imaging techniques to amplify and re-direct the fluorescing light back onto the cell for treatment. This technique has the advantages of both chemical and physical techniques: many cells can be accessed simultaneously with chemical tagging, while cell destruction takes place only from the amplified and refocussed light.
It is therefore desirable to relax the chemical restrictions imposed by chemotherapy and photodynamic therapy by using selective tagging of the undesirable cells, followed by a non-chemical technique for tagged cell destruction.